1. Field of the Invention
This invention relates to semiconductor lasers and more particularly to a method and means for providing a choice of a plurality of collimated beam lasers having specific qualities for a multiplicity of applications requiring specific attributes of wavelength, polarization, and beam shape characteristics including expanded or reduced circle and broad or thin line characters. A choice of a plurality of focused beam lasers is also provided.
2. Description of the Prior Art
In the Near Infrared, 780-830 nanometer range lasers and including 670 nanometer laser, the polarization of the radiation is oriented parallel to the junction of the semiconductor laser; that is, along the minor axis with respect to the elliptical beam divergence of the semiconductor laser. The radiated beam can first be collimated and then expanded simply by using two prisms oriented along the minor axis of the beam, without any antireflection coatings on the hypotenuses of the prism pair for transmitting the TM mode without loss. An enlarged collimated circular beam results. An anti-reflection coating is placed on the hypotenuse of each prism to increase the polarization ratio; this principle is described in U.S. Pat. No. 4,609,258; to Adachi and Yamada. The enlarged, collimated round beam contains all the energy radiated by the TM polarizations of the beam.
If the prisms are placed in reverse order with respect to the laser; that is, rotated 180 degrees, with the right angle side perpendicular with respect to the radiated beam, with an antireflection coating on the hypotenuse of each prism, a shrunken circular beam spot is produced, and both TM and TE modes are passed without loss. These principles are expounded in the Adachi patent 5,321,717.
In addition, the following papers are important insofar as the resultant TE and TM modes of operation in semiconductor lasers is concerned:
Semiconductor Science and Technology; G. G. Forstman et. al. Pages 1268-1271; "Effects of Strain and GalnP.sub.2 Superlattice" ordering on laser polarization. PA0 IEEE Journal of Quantum Electronics, Vol. 24, No 12 Dec. 88 "Optical Gain in a Strained-Layer Quantum-Well Laser"; Doyeol Ahn and Shun-Lien Chuang PA0 Electronic Letters, 31 Mar. 84; Vol 30 #7, Pg 566-8 "Low Threshold Operation of Tensile-Strained Galn/AIGalnP MQW LDs Emitting at 625 nm"; Tanaka, Yanagisawa, Takamoto, Yano and Minagawa. PA0 1) wavelength changes, using both the Multiquantum Well 635 nanometers, and Index-guided 670, 780, and 830 nanometer lasers for example. The wavelength can be changed by switching the semiconductor module for the desired wavelength semiconductor. PA0 2) beam spot shaping and polarization indexing, This is done by the 180 degree orientation reversal of a two-prism beam shaper for expanding the beam spot or reducing the beam spot size. PA0 3) Polarization of the image is determined by a combination of the semiconductor laser having a desired polarization direction and the beam shaper having the desired transmission characteristics, and orienting the semiconductor for the desired beam spot image. PA0 4) Providing the objective optics; i.e., the .backslash. /2, .backslash. /4 etc. wave plate to transmit a collimated beam, or optical lens focusing the beam or expanding the beam to provide a choice of eight different combinations constituting eight unique laser beam sources.
The invention provides a means for selecting laser parameters to control the characteristics of the beam for specific applications. The combination of the focusing lens with the above mentioned beam can have such applications as requiring resolution of upwards of 1600 lines per inch as with a long working distance. Such applications exist in photoscanners, and high resolution laser printing. In manufacturing of Integrated Circuits, submicron resolution of a focused spot is required. Also, in the area of high density compact disk, a submicron size focused spot is required.
The invention also provides a general solution to beam spot image selection that is easily accomplished by a simple means that can be adapted to existing systems to provide beam shape size, and polarization selection for existing practical commercial laser wavelengths. If the novel laser device is used with a multiquantum well visible laser, an even smaller spot can be obtained, or a small thin line segment can be formed. The focused beam can be made smaller in proportion to the wavelength and the polarization can be selectable. Alternatively, the beam can be made large in an expansion mode producing a large beam spot or a broad line segment based upon the semiconductor junction and beam orientation.